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Galloping Glaciers

North America boasts 104 surge glaciers. No one knows why these glaciers behave so differently from normal glaciers; they certainly look the same. But while ordinary glaciers creep along a few inches per day, surging glaciers will sometimes charge ahead at the rate of several yards per hour. The surges may be years apart; and they may occur periodically. The surges start high up on the glacier and propagate down to the foot, which plods along a few inches per day until the surge arrives. Then, it leaps forward, only to return to normality until the next periodic surge. The surges seem to occur when water spreads out under the ice, lubricating its flow. Beyond this we know little.

Why do some glaciers surge while those right alongside behave normally? Are the surges really cyclic? The Variegated Glacier, in Alaska, for example, surged in 1906, probably in 1926, in 1947, in 1964-65, and in 1982 -- about 20 years between surges. The surges do not seem to be connected to earthquakes, climatic changes, volcanic heat, or anything obvious.